Specifications of a neutron exposure accelerator system for biological effects experiments (NASBEE) in NIRS

We developed a neutron irradiation facility, neutron exposure accelerator system for biological effect experiments (NASBEE) for biological studies in National Institute of Radiological Sciences, Japan. Irradiation field of 2 MeV average neutrons generated by a Be(d–n)B reaction is established. Dose uniformity of 240 mm in diameter irradiation field is producible within ±2.5% with a dose rate of 0.87 Gy/h at sample target distance of 1170 mm. Two irradiation rooms, a specific pathogen-free (SPF) conditioned one and a conventional, are now available. Irradiation protocols for in vitro experiments are now established and demonstrated by obtaining a relative biological effectiveness (RBE) of cell inactivation measured to be 3.54 with 10% survival dose (D₁₀).     

Palladium-catalyzed C-H homocoupling of bromothiophene derivatives and synthetic application to well-defined oligothiophenes

Synthesis of oligothiophenes of well-defined structures that possess 2-8 thiophene units is performed with a new synthetic strategy involving C-H homocoupling of bromothiophenes and cross-coupling with organostannanes. Tolerance of the carbon-bromine bond to the palladium-catalyzed C-H homocoupling results in oligothiophenes bearing C-Br bonds at the terminal thiophene rings, which allow further transformation by the catalysis of a transition-metal complex.     

Reconstruction of Scalar Source Intensity Based on Sensor Signal in Turbulent Channel Flow

We consider a turbulent channel flow, where a scalar point source with a time-harmonic intensity releases a substance that can be modeled as a passive scalar. With the source location known, our objective is to estimate the time history of the source intensity based on sensor measurements at different locations downstream of the source by adopting an adjoint approach. It is shown that the proposed algorithm reproduces the original coherent sinusoidal wave of the scalar source accurately from the chaotic scalar signals measured by our sensors. By systematically changing the source-sensor distance and the pulsation frequency of the source, we clarify how these two factors affect the estimation accuracy. The proposed scheme is also applicable to estimation with multiple sensors. We demonstrate that increasing the number of sensors improves the estimation greatly when the scalar is released from a source away from the wall, where large-scale eddies dominate the scalar dispersion. In contrast, the estimation performance remains poor even with multiple sensors when the scalar source is located near the wall, where the source information is quickly lost due to the strong turbulence activity and the scalar diffusion in the near-wall region.     

Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the m(s)=±1 sublevels differs significantly from that of the m(s)=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor (29)Si nuclear spin. We measure the coherence time of the (29)Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance.     

Luminescence of GaN single crystals prepared by heating a Ga melt in Na–N2 atmosphere

Colorless transparent prismatic crystals (0.5‐2.0 mm long) and hopper crystals (1.0‐2.5 mm long) of GaN were prepared by heating a Ga melt at 800°C in Na vapor under N₂ pressures of 7.0 MPa for 300 h. The photoluminescence (PL) spectrum of a prismatic crystal at 4 K showed the emission peaks of neutral donor‐bound exciton (D⁰‐X) and free exciton (X_A) at 3.472 eV and 3.478 eV, respectively, in the near band edge region. The full‐width at half‐maximum (FWHM) of (D⁰‐X) peak was 1.9 meV. The emission peaks of a donor–acceptor pair transition (D⁰‐A⁰) and its phonon replicas were observed in a lower energy range (2.9‐3.3 eV). The emission peaks of the D⁰‐A⁰ and phonon replicas were also observed in the cathodoluminescence (CL) spectrum at 20 K. The (D⁰‐X) PL peak of a hopper crystal at 4 K was at 3.474 eV (2.1 meV higher), having a FWHM of 6.1 meV which was over 3 times larger than that of the prismatic crystal. A strong broad band with a maximum intensity around 1.96 eV was observed for the hopper crystals in the CL spectrum at room temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Estimation of single-nucleotide polymorphism allele frequency by alternately binding probe competitive polymerase chain reaction

A modified solvent microextraction with back extraction method (SME/BE) combined with high performance liquid chromatography and fluorescence detection (HPLC-FD) was developed for the determination of citalopram in human plasma. Extraction process was performed in a home-made total glass vial without using a teflon ring, usually employed in SME/BE. Citalopram was first extracted from 0.5 mL of plasma, modified with sodium hydroxide, into hexane. Back extraction step was then performed into 5.2 μL of 45 mM ammonium formate solution (pH 4) using a GC microsyringe. The extract was subsequently transferred into a liner-like vial and then injected into the HPLC system. An enrichment factor of 150 along with a good sample clean-up was obtained. The calibration curve showed linearity in the range of 1.0–130.0 ng mL⁻¹ with regression coefficient corresponding to 0.992. This range covers therapeutic window and even lower amounts which is important in pharmacokinetic studies. Limits of detection and quantification, based on a signal to noise ratio (S/N) of 3 and 10, were 0.3 and 0.8 ng mL⁻¹, respectively. The method was also applied for the determination of citalopram in plasma samples after oral administration of 40 mg single dose of citalopram.     

Preparation of polysiloxanes from silicic acid. V. Condensation of silicic acid butyl esters and formation of silica fiber from the ester solutions

The condensation of silicic acid butyl esters was investigated by gel permeation chromatographic (GPC) analysis. The results revealed that the condensation was greatly dependent on a degree of esterification of the esters. The ester with the lowest degree of esterification underwent condensation to form a highly polymerized ester. It was found that fibers could be drawn from the ester solution before gelation.     

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

High-precision vector and tensor analyzing powers of elastic deuteron-proton ( d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70^°-120^° in the center-of mass frame for incident-deuteron energies E _d ^lab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(2⁺) reaction at 0^°. Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high-precision data consistently and requires, therefore, further investigation.     

Measurement of the vector A y and tensor A yy , A xx , A xz analyzing powers for the dd → 3H p reaction at 200 MeV

The data on the vector A _y and tensor A _yy , A _xx , A _xz analyzing powers for the d → ³H p reaction have been obtained at the energy of the initial deuteron of 200MeV in the angular range of 0–95 degrees in the c.m.s. The calculations performed within one-nucleon exchange model with the use of the standard three-nucleon bound state wave functions fail to reproduce the data on the tensor analyzing powers.     

Evolution of the Kondo effect in a quantum dot probed by shot noise

We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2.